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I've got a fairly large deck that sits, in part, on a hillside. Over the past years the soil is eroding away such that I'm getting worried about the outermost posts. I know I need to put a good amount of dirt back onto the hill side to build it back up. It probably needs to be done in stages too in order for it to settle properly before doing hardscape. The question is how to prevent the erosion from happening again. One challenge is that the base of the hillside is a seasonal creek that flows in the winter. The water doesn't come up the hill very far and it doesn't "flow" against the hill; more so just rests against it. But if you were to build a retaining wall all the way at the base of the hill, it would be exposed to the creek flow. Looking at the picture

The area is almost in shade the entire day and it's under a eucalyptus tree which dumps all kinds of crap around it so getting things to grow is difficult. I think the best thing to do would be to build a terraced retaining wall starting at the base of the hill back up. That'd be a large and expensive project so I'm not super excited about that option.

My latest idea would be to rebuild the hillside with fill dirt and then dump some 4"-6" gabion granite stones on top of the entire hillside. I'm talking the loose stones, not the cages with rocks you commonly see. I still worry those 4-6" stones are not large enough to stay put. So maybe I need bigger stones? My idea is based off of what I've seen around the edges of rivers and lakes sometimes. Is the stone idea going to work? Any suggestions/advice would be appreciated. Thanks!

Please ignore the square pavers in the photos. I know they will do absolutely nothing to help.

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You might need a professional here, because my suggestion is indeed a retaining wall. What you do in cases like this is build the wall down to a solid footing. Make sure they put rods into the hillside to both hold the wall in place and help stay the soil. The wall will better resist the water and stop the erosion. Check with local regulations, but you can certainly build walls down into a creek bed structurally.

  • That's what I was afraid of. Is the rock idea just a hack or somewhat temporary solution? My guess would be that the retaining wall would be super expensive given the engineering needs, material movement, limited access and size. You can't tell from the pictures but the same sort of thing would need to be done on the other side of the tree. – user1985112 Sep 25 '18 at 15:57
  • The rocks won't hold for long, if at all. Retaining walls are designed for this sort of thing. – Machavity Sep 25 '18 at 16:16
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I’d use shotcrete.

Shotcrete is concrete sprayed on the ground to protect the hillside.

It’ll be about 1/10th the cost of a retaining wall and completed in about 1 day.

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